Such a sheet conveyor is described, for example, in the patent application DE 198 44 271 C1. The essential elements of the known sheet conveyor are an outer ring having a friction coating and a toothed wheel of smaller diameter that constantly meshes with the inner toothing of the outer ring. The outer ring is set into rotation by the toothed wheel and placed onto the sheet stack by a force having a force component in order to displace the uppermost sheet of the stack. The contact point of the outer ring on the sheet in reference to the direction of conveyance TR is always behind the engagement point of the driving toothed wheel in the inner toothing of the outer ring so that the sheet is pulled. When the sheet is blocked, the outer ring is raised above the driving toothed wheel, so that the friction force between the friction coating of the outer ring and the sheet to be conveyed is reduced.
The known sheet conveyor comprises two lever systems, namely a first lever system that enforces the tooth engagement between the toothed wheel and the inner toothing of the outer ring and determines the contact force on the sheet as well as a second lever system that has an effective connection with an optical sensor and serves for detecting the deflection of the outer ring. The contact force of the outer ring on the sheet varies depending on the deflection of the lever and increases continuously. The necessary contact force of the outer ring amounts to approximately IN, thus necessitating a plurality of motor steps until this force is reached. Should the sheet stack be compressed by the contact force, the contact force is reduced and the required contact force of approximately IN decreases.
A similar device is known from the patent application U.S. Pat. No. 6,193,232 B1.